nsantolick

Greetings and Salutations;


I'm researching appropriate tires for my car, a 1989 928S4 with an automatic transmission.

I'm fitting factory Porsche 7x17 ET50 & 9x17 ET55 sized wheels.

Been playing with the tire/wheel fitment spreadsheet and am probably going with 225/45 17's & 255/40 17's respectively. Seems like a good fit and no spacers should be required. I wonder though if it'd be a good idea to still use them in the rear - that perhaps the car would handle/track better?

With those sizes in mind, I've been researching available tires and seem to be drawn to my favorite, the Pirelli P-Zeros.

Has anyone tried out these "RFT's" on a similar car? Has anyone used ANY make of "run flat tire" on their cars?

It seems that tire pressure monitoring systems are highly recommended when using run flat tires. I've never used such a tire, and understand the warning but wonder if I'd really not notice loss of pressure on my own should it EVER occur.

Retrofitting Porsche's system seems to be a no-no, from what I've gathered perusing the forums here. Some aftermarket recommended systems that have been mentioned are no longer available so while I'm at it, I'm curious what the consensus is here about the need for them, as well as if there's any newer products worth considering.

I appreciate the potential for not being stranded and have always loved P-Zero's. I'm just wondering if I really should bother with fitting some sort of monitoring system. I really don't want anything permanently plugged into the cigarette lighter and don't want to be fastening anything to the dashboard. I'm not quite into the models with keychains either. Perhaps I can live with installing something near the parcel shelves but ideally I'd like something that could be put in the center console storage area, or even the glove box. Bummer that the original Porsche system is "out..."

Any comments/advice/recommendations would be most appreciated. I'd like to order "whatever I need" immediately. I've done a lot to my car lately and am about to put it back into full-time service.

Thanks in advance for any input. All the best...







Nick - Philadelphia, Pa.
1989 928S4 Grand Prix White Auto

borland

TireRack.com rates tires and provides customer comments.

martyp

I've heard (from the BMW crowd, so take it with a grain of salt ) that cars with factory run flats have a suspension that is "tuned" to work with the stiffer sidewalls and greater weight. IIRC the recommendation was to not use RFTs on a car without the "correct" suspension, but you could use non-RFTs on a car with RFT tuning, albeit with some ride roughness. YMMV, and maybe someone here with more experience will chime in. Good Luck!

nsantolick

tirerack.com currently offers only two TPMS's and one of them uses the caps that just screw on. I really want a type that houses the sensors inside the wheels and don't really like the one they offer, at least compared to some others I've seen.

I'm digging around right now actually and found the "Orange Electronic P409S" - it seems like a great unit and isn't very expensive at all. It simultaneously displays readings for all tires in LED and monitors temperature as well. It got decent reviews on Amazon, where it appears to be in stock, and even ships free.




If I get that one, I'm considering mounting it over my LCD clock on the center console (or possibly even recessing it there - I hate the redundancy of a clock there with my aftermarket stereo system) but ideally I'd love to hide it in the center console - unfortunately I'd probably not hear it if it sensed a flat.

FYI: I just discovered that these tire pressure monitoring systems are federally mandated on cars fitted with original equipment run flat tires starting with the 2008 model year.

I'm really torn. I can't recall ever getting a flat tire on one of my cars. I can't imagine not noticing one if I did, even with heavy-walled run-flat tires. At the same time, these systems seem quite recommended with run-flat tires and aren't all that expensive lately.

Anyway, if I want to stick with P-Zero's, with these tire sizes, I don't seem to have much of a choice other than to use their run flat tires...

Bill Ball

225/45 x 17 on the front is BARELY going to fit with a 50ET wheel (such as the 2002 996 wheels in my avatar pic), I hope. That's what I just got in Dunlop Direzza Sport Z1 Star Spec, another tire you should consider. Looks like they could hit the fender with the suspension compressed by a bump in a fast turn. I had previously run 205/45 on the front with no problem, but that slim of a width is not available in that tire. I certainly prefer the 225s as long as they clear the fender. Anyway, these Dunlops are very highly rated, about $250 less than the Pirellis and have very stiff sidewalls, almost like runflats. Another local owner ran on 2 flat Dunlop Z1s and did not notice for quite a while, so I can see the need for a pressure monitor.

fbarnhill

I have used the P0s a couple of times. I love the way they handle but hate the way they wear. Maybe I just was too rough on them but it sucks to have them wear out so often.

nsantolick

Frank;

What kind of mileage did you get out of your P-Zero's? I last ran them on Mustang Cobras and, lol, got about 7,000 miles until they were below spec. I believe I hit 12-13,000 once, but they were largely down to fabric at that point.

I'd be thrilled to see 15,000 or so with the S4 but really don't know what to expect. I mostly will be doing highway driving, it seems. Just curious what kind of mileage you experienced...

fbarnhill

Yep, that is about right. It seemed like I just put them on, and they were quite expensive, and I look at the back tires and they were slick... That sucks. Now, I must say that I thoroughly enjoyed them. I am guessing 7 -10k miles. It was just about one year.

nsantolick

"The tire that handles twice as well lasts half as long. And our Pirelli's handled oh so well..."

Didn't Rutger Hauer say that in the remake of Blade Runner???

bigmac

Am running 275/17 rears on my S4, just clear. Not sure that with a new MURf S/C, that they will be enough.

SteveG

Car came with P zeros, not RFT. F: 225/45 R 255/40. They look great. Lots of road noise; I'm getting lots of spin (they are near end of life). I'm going to try Michelin Pilots this time around-- as in this week.

c_span

Over here at least, BMW (who have been the big proponents of run-flats) have struggled to make their cars ride adequately since enforcing them onto their range. Many owners dump them for non-runflats at the first tyre change.

They are getting "better" (in terms of suspension tuning on each new BMW) but that won't help on a 928 which wasn't designed for tyres with such stiff sidewalls. I would avoid, personally..

nsantolick

Okay, now I'm wondering - trying to "understand this", you know. What's the difference to "a suspension" whether sidewalls are extra stiff because of being designed to "run flat" or of a significantly lower profile tire than was originally assumed?

I just don't understand the difference as far as the spring rates and dampening of the suspension are concerned. Going from a 45 to a 30 series tire versus a softer to more rigid sidewall. Aren't either similar in inherent "springiness?"

c_span

Manufacturers do work extensively with tyre makers when developing new models, in order to match the compound and tyre characteristics to the car and its suspension design.

In terms of secondary ride you would factor in springs, dampers, bushings *and* the tyre (and probably the seat cushioning as well!) as these all combine to give the overall compliance in the ride and contribute to the comfort of the occupants. The runflat tyres have sidewalls stiff enough to prevent the rim touching the road in the event of a puncture, so by definition these have to be much stiffer than normal tyre.

Mind you, it depends on how good the roads are near you! In London, they're pretty poor condition these days with lots of holes and poor surfaces especially after winter. I'm very glad to be non-RDK now and able to take my rears down to a more reasonable pressure where I don't feel every leaf and imperfection in the road!

nsantolick

Okay. The aforementioned TPMS has been ordered. I'm still up in the air about tires. Size. Brand. Run-flat or not...

I'm actually planning on starting another thread later, as my research has just led to a couple more questions that don't seem to be touched on much, concisely, anyway.

Anyway, I'm pretty excited, after all, to add this Orange brand tire pressure monitoring system to my car. It'll be interesting to see how it all turns out. Looks like it could integrate well, and be easily reversed. I'm kind of curious to monitor the effects of this and that on the tire temperatures particularly...

More to come...






Nick - Philly... '89S4